• 创建watcher.json文件，放在consul配置目录下，启动consul时指定-config-dir

{
  "watches": [
    {
      "type": "key",
      "key": "foo/data",
      "handler_type": "http",
      "http_handler_config": {
         "path":"http://127.0.0.1:8763/watch",
         "method": "POST",
         "header": {"x-foo":["bar", "baz"]},
         "timeout": "10s",
         "tls_skip_verify": false
      }
    }
  ]
}

• 创建一个http服务用于接收变更的key，http://127.0.0.1:8763/watch

    @RequestMapping("/watch")
    public void watcher(HttpServletRequest request) throws IOException {
        System.out.println(request.getMethod());
        BufferedReader reader = new BufferedReader(new InputStreamReader(request.getInputStream()));
        String str = "";
        String wholeStr = "";
        while ((str = reader.readLine()) != null) {
            wholeStr += str;
        }
        System.out.println("body:" + wholeStr);
    }

• 在consul ui中新增 或者修改foo/data这个key值，watcher就会收到这个更新后的值

POST
body:{"Key":"foo/data","CreateIndex":12,"ModifyIndex":12,"LockIndex":0,"Flags":0,"Value":"YWFhYWFhYQ==","Session":""}
POST
body:{"Key":"foo/data","CreateIndex":12,"ModifyIndex":17,"LockIndex":0,"Flags":0,"Value":"YWFhYWFhYXNzc3NkZHNkZHNk","Session":""}
POST
body:{"Key":"foo/data","CreateIndex":12,"ModifyIndex":25,"LockIndex":0,"Flags":0,"Value":"ewogICJ0ZXN0IjoidGVzdCIsCiAgInRlc3QyIjoidDMzM2VzdCIKfQ==","Session":""}

value为base64编码，解码后得到需要的值。

• handle除了是http，还可以是sh脚本，如

  {
    "type": "key",
    "key": "foo/bar/baz",
    "handler_type": "script",
    "args": ["/usr/bin/my-service-handler.sh", "-redis"]
  }

  以下摘自官网：https://www.consul.io/docs/agent/watches.html#key

• Watch Types/支持的类型

  The following types are supported. Detailed documentation on each is below:

• key - Watch a specific KV pair
• keyprefix - Watch a prefix in the KV store
• services - Watch the list of available services
• nodes - Watch the list of nodes
• service- Watch the instances of a service
• checks - Watch the value of health checks
• event - Watch for custom user events

{
  "type": "key",
  "key": "foo/bar/baz",
  "args": ["/usr/bin/my-service-handler.sh", "-redis"]
}

{
  "type": "keyprefix",
  "prefix": "foo/",
  "args": ["/usr/bin/my-service-handler.sh", "-redis"]
}

{
  "type": "service",
  "service": "redis",
  "args": ["/usr/bin/my-service-handler.sh", "-redis"],
  "tag": "bar"
}

等等